Jews and Christians
If you doubt what We have revealed to you, ask those who have read the Scripture before you.
10:94And if thou (Muhammad) art in doubt concerning that which We reveal unto thee, then question those who read the Scripture (that was) before thee. Verily the Truth from thy Lord hath come unto thee. So be not thou of the waverers.
16:43And We sent not (as Our messengers) before thee other than men whom We inspired - Ask the followers of the Remembrance if ye know not! -
21:7And We sent not (as Our messengers) before thee other than men, whom We inspired. Ask the followers of the Reminder if ye know not?